Drilling fluids



Patented Feb. 13, 1945 2,369,-i? ammo moms William W. Robinson, In, LosAngeles, Calif., as-

signor to The Texas Company, New York, N. Y., a corporation of DelawareNo Drawing. Original application May 17, 1935,

Serial No. 21,978. Divided and this application Maw 13, 1944, Serial No.518,117

it Claims. (Cl. 252-85) This invention relates to drilling muds and moreparticularly to the preparation of drilling muds employed in thedrilling of wells.

This application is a division of my application Serial No. 21,978,filed May 17, 1935. 1

In its broadest aspect, my invention contem-' Drilling muds are almostuniversally used in the drilling of wells employed for tappingunderground collections of oil, gases, brines, and water.

These muds fulfill various functions, the most important of which are toassist in the removal of cuttings from the wells, to seal ofi gaspockets which may be encountered at various levels, and to lubricate thedrilling tools and the drill pipes which carry the tools.

Drilling muds are essentially mixtures of clay and water, usually socompounded that they weigh from eight to twelve pounds per gallon.Whenever it is found necessary to increase the specific gravity of aparticular mud, it is customary to add thereto finely-divided materialswhich have a highspecific gravity such as barytes, etc. r

An ideal drilling mud is one which is thixotropic, that is to say, afluid which, on agitation by pumping. or otherwise, has a relatively lowviscosity and is iree-flowing but, when agitation is stopped, graduallysets or gels. This gelling ill strata containing gases under highpressurl When drilling through such strata, the hydro static head of thedrilling mud serves normally t more than counterbalance the gas pressurrDuring the drilling operations, when it become necessary to withdraw thedrill pipe and th drilling tools, the non-thixotropic drilling mu willcling thereto. In this manner the balanc that has existed between thehydrostatic head 0 the drilling mud and the gas pressure is disturbeand, if the gas pressure is higher than the lee sened hydrostatic headof the drilling mud, a ge blowout occurs.

Drilling muds consist essentially of colloid: dispersions of clay inwater. When this is con slde'red, in conjunction with the further factthe the thixotropic character of a drilling mud is function of itscolloidal condition, it become obvious that the clay particles, having asiz within the colloidal particle size range, determin largely thethixotropic character of a drillin mud. The aforementioned colloidalparticles clay are essentially acids whose anion is a mice is strongenough to support them. When such a drilling mud is circulated through awell, it 7 picks up the cuttings and carries them to the surface andthere, upon'settling in a settling pit, the cuttings settle out, leavinga substantially cuttings-free drilling mud;

The use of, a drilling mud, which is not thixotropic, isattended by manydisadvantages, the

, that the use of a non-thixotropic drilling mud may cause gas blowoutswhere the well traverses of the general formula 'X(A1203) -Y(SlO2)Z(H2o)where X is approximately 1, Y is approximate] 3, and Z may vary overwide values. I

In the interests of simplicity, the aforemer tioned anion will be termedhereinafter as 012 and the compounds formed by its combinatic withvarious cations will be termed clays of suc cations; so, for example,the hydrogen compour will be termed hydrogen clay or acid clay, tlsodium compound will be termed sodium cla while the calcium compoundwill be called ca cium clay. For purposes of this; discussion, vconsider three types-of clays, acid clays, clays 4 monovalentions suchas sodiumclays and mult valent clays such as calcium or magnesium clayIt has been observed that dispersions in wat of either acid clays ormultlvalent ion clays ter to gel with great rapidity and are easilycoag1 lated. It is obvious that such types of dispersiol are difllcultto use as drilling muds.

The deterioration of thlxotropic drilling mu involves the conversion ofa monovalent clay in either an acid clay or a multivalent ion cla Theformer occurs when the thixotropic drillll mud encounters acid stratawhereby the hydr gen ions of thestrata displace the vdesiral:

,monovalent ions of the cla resulting in the to mation of an acid clay.--'I 'he latter type of dete ioration, which is much more common, newwhen a drilling mud encolmters strata of calciu and magnesium compounds.Under such circumstances, the phenomenon, known as base exchange, occurswhereby the monovalent ion clays of the thixotropic drilling mud areconverted into multivalent ion clays.

I have discovered that by incorporating sodium hexametaphosphate in athixotropic drilling mud under the conditions described below, thedrilling mud may be made more stable against deterioration by baseexchange. Sodium hexametaphosphate is usually ascribed the formula(NaPOshs, and. is available commercially in a form which upon solutionin water gives an alkaline reaction.

Not only may sodium hexametaphosphate be employed for renderingthixotropic drilling muds more stable against base exchange, but it mayalso be employed as described below for converting a drilling mudcontaining multivalent ion clays into drilling muds having thecharacteristics of muds containing desirable monovalent ion clays. So,for example, by treating a drilling mud containing a calcium clay withsodium hexametaphosphate, it may be converted into one having thecharacteristics of a drilling mud containing a sodium clay.

In accordance with the invention, the sodium hexametaphosphate ispreferably employed in proportions corresponding to 0.001 to 0.1% byweight of the drilling mud. The use of sodium hexametaphosphate in anamount within this range is usually surficient to accomplish the desiredresults; while, at the same time, overtreat merit of the drilling mud isavoided. it will be understood, of course,that the optimum amount to beused in a given case will depend upon the I specific characteristics ofthe drilling mud in question.

It has been found that drilling muds, consistins essentially ofdispersions of monovalent ion clays in water, are particularly valuableas drilling fluids when they are maintained within a particular range ofpH concentrat on. which range may be in the neighborhood oi from 8.0 to11.5. In order that drilling mud, treated with sodium hexametaphosphate,may be maintained within this range-of pH concentration. ll preferablyemploy, in connection with the hexa= metaphosphate salt, a bufier saltor buffer salt mixture such, for example as salts of weak acids as sodum carbonate. dlsodium phosphate or the like. or balanced mixtures ofhydroxides such as sodium and lithium hydroxides, or similar bydroxideswith correspond ng salts of such acids as boric, phosph ric, carbonic,oxalic, silicic, and similar weal; acids.

When electrolytes are dissolved in a drilling mud. they may, to alimited extent. cause a slight coagulation of the drilling mud.Therefore, when employing either sodium hexametaphosphate alone or incombination with a buffer salt or a buffer salt mixture. I find itdesirable to minimize the coagulation effect of this salt on thedrilling mud, by incorporating therein a lyophile colloid such asquebrach straw emulsion, dextrin, casein, catechu, and similarmaterials.

Accordingly, exceptionally valuable drilling muds of the invention arealkaline thixotropic dispersions comprising clay, water, sodiumhexametaphosphate and a buffer salt or a bufier salt mixture adapted tomaintain the dispersions in an alkaline state. Especially preferreddrilling muds of this class also contain a lyophile colloid.

In order that those skilled in the art may more readily appreciate theparticular effectiveness of sodium 'hexametaphosphate, I offer herewiththe viscosities in seconds of the treated samples when accuser resultsof comparative experiments in which a non-thixotropic calcium claydrilling mud was treated with various types of inorganic compounds. Thedrilling mud employed when tested in the Marsh funnel viscosimeter,using 300 cubic centimeter samples, wasfound to have a viscosity oi?67.5 seconds. The mud was then treated with 0.001, 0.01 and 0.1percentage by weight of the compounds indicated in the followin table.The figures appearing in the three columns are the tested in the Marshfunnel viscosimeter.

Seconds Seconds Seconds Trlsodium phosphate 65. 6 49. 43. 0 Disodlumphosphate 58. 0 47. 5 35. 5 Sodium hexamctaphosphatc 40.0 26. 0 18.0Orthophosphoric ecicl o 40. 0 34. 0 35. 0 Soda ash 56. 0 63. 5 l8. 0

Since viscosity is a direct measure of the desirability of a drillingmud, it is obvious from the foregoing table that sodiumherametaphosphate is an effective agent for the treatment or calciumclay drilling muds.

My invention may be carried out in several different Ways. For example,I may prepare a thlxotroplc drilling mud which is substantially immuneto deterioration. by base exchange by forming a dispersion oi a suitablemonovalent ion clay in Water and adding to the so-formed drilling mud. aquantity of sodium hexametaphoa pirate sufiicient to maintain theviscosity of the mud relatively constant during use. I also con templatethe continuous addition of sodium hex-- ametaphosphate during use tomaintain it in the proper condition. My invention may also be eniployedfor converting drilling muds which have been deteriorated by baseexchange into non-- thixotropic drilling muds, and l accomplish thisresult by adding to the deteriorated drilling mud a sufficient quantityof sodium hexametaphos phate to restore it to a tliixotropic state.

As a. further application of my invention, it contemplate the use ofsodium hexametaphosphate in connection with drilling muds containingbentonites. This type of drilling mud has found substantial useparticularly in wells where heaving shale is encountered. However,drilling.

Aquagel. A typical analysis of this bentonite is as follows:

Per cent Silica "a 49.52 Iron oxide 2.42 Aluminum oxide 16.71 Calciumoxide 4.40 Magnesium oxide 5.07 Sodium and potassium oxides 4.49Moisture 9.85 Combined water and volatile matter 6.64 Sulfuricanhydrlcle 0.45 0.46

Chlorine Five dispersions were prepared containing respectonite inwater. Th viscosities of these dispersions were obtained by means of theStormer viscoslmeter and are reported in the following table incentipoises.

and the viscosities of the so-treated dispersions again determined. Theviscosities in centipoises are listed in the third column of thefollowin table:

Absolute Ziscositlydoi' quage 1sgggg persion 0011- I Percent of Aquageldispersed in water y taluing 1% by volume of dlspersmn 10% solution ofsodium hexametaphosphate Centipuises Centipoises The above resultsclearly indicate the value of sodium hexametaphosphate for maintainingthe thixotropic character of a bentonite dispersion. Similar efiectsmaybe secured by treating drilling muds containing ordinary monovalention clays to which have been added varying percentages ofbento'nite'clays. W.

Obviously many modifications and variations of the invention ashereinbefore described may be made without departin from the spirit andscope thereof, and therefore only such limitations should be imposed asare indicated in the appended claims.

I claim:

1. A drilling mud in the form of an alkaline thixotropic dispersioncomprising clay, water, sodium hexametaphosphate, and a buffer saltadapted to maintain the dispersion in an alkaline state.

2. A drilling mud in the form of an alkaline thlxotropic dispersioncomprising clay, water, sodium hexametaphosphate, a lyophile colloid,and a butler salt adapted to maintain the dispersion in an alkalinestate.

To samples of the respective dispersions theremzasihm added 1% by yoiumeof a solution of sodium hexametaphosphate 3. The method oftreating acirculatingdrilling tively 1%, 2%, 4%, 6%, and 7.75% of the hen mudconsisting of an alkaline thixotropic dispersion comprising clay andwater employed in the drilling of a well, which comprises adding to saiddrilling mud sodium hexametaphosphate and a bufier salt adapted tomaintain said drilling mud in an alkaline state.

4. The method of treating a circulating drilling mud consisting of analkaline thixotropic dispersion comprising clay and water employed inthe drilling of a well, which comprises adding to said drilling mudsodium hexametaphosphate, a lyophile colloid, and a bufier salt. adaptedto main;

tain said drilling mud in an alkaline state.

5;A drilling mud comprising clay, water and from 0.001 to 0.1% by weightof sodium hexametaphosphate.

6. A method of converting-a prising multivalent ion clay and water to athixotropic drilling mud which comprises adding thereto from 0.001 to0.1% by weight of sodium hexametaphosphate.

' 7. A drilling 'mud' in the form of an alkaline thixotropic dispersioncomprising clay, water, from'0.001 to 0.1% by weight of sodiumhexametaphosphate, and a bufier salt adapted to maintain the dispersionin an alkaline state.

8. A drilling mud in the form of an alkaline drilling mud com- Ithixotropic dispersion comprising clay, water,

from 0.001 to 0.1% by weight of sodium hexametaphosphate, a'lyophilecoll'oid. and a butler salt adapted to maintain the dispersionin an alkaline state.

9. Themethod of treating a circulatinmng mud consisting of an alkalinethixotropic dispersion comprising clay and water employed in thedrilling of a well, which comprises adding to said drilling mud from0.001 to 0.1% by weight of sodium hexametaphosphate, and a bufier saltadapted to maintain said drilling mud in an alkaline state.

10. The method of treating a circulating drilling mud consisting of analkaline thixotropic dispersion comprising clay and water employed inthe drilling of a well, which comprises adding to said drilling mud from0.001 to 0.1 by weight of sodium hexametaphosphate, a lyophile colloid,and a buifer salt adapted to maintain said drilling mud in an alkalinestate. I

WILLIAM W.IROBINSON, in.

